The invention relates to fuel injectors and more particularly to methods of attenuating noise and vibration created by fuel injectors.
Electromagnetic fuel injectors are common in modern fuel-injected internal combustion engines. The fuel injectors deliver fuel to the engine in metered pulses which are appropriately timed to the engine operation. To produce the metered pulses of fuel, electromagnetic fuel injectors typically include a metallic valve member that is actuated by an electromagnetic coil to open and close the fuel valve. When the valve member is actuated to open the fuel valve, the top portion of the valve member, or armature, reaches its upper limit of travel and strikes a metallic support tube. The metal-to-metal contact sends an impulse through the injector that is radiated from the exterior surface of the injector as noise and vibration.
Likewise, when the valve member closes the fuel valve, the bottom portion, or valve ball, reaches its lower limit of travel and strikes a metallic valve seat. Again the metal-to-metal contact sends an impulse through the injector that is radiated from the exterior surface of the injector as noise and vibration.
Recent advances in vibration and background noise reduction inside the passenger compartment of vehicles have increased the demand for quieter running engines. Reduced background noise in the passenger compartment has made previously inaudible engine noises, such as injector noise, audible. Only recently has injector noise begun to spark serious consumer complaints.
Various attempts have been made to reduce the noise and vibration emanating from fuel injectors. As time has passed, the methods have become more complex and more expensive. One early attempt, U.S. Pat. No. 5,094,217 disclosed an insulating housing that encircles and encloses at least a portion of the fuel injectors to deaden the sound.
More recently, U.S. Pat. No. 5,823,446 disclosed the use of an elastomeric ring disposed between the bushing and the valve body to provide an insulating layer tending to dampen noise and vibration when the valve is open and fuel is flowing therethrough.
Even more recently, U.S. Pat. No. 5,967,419 disclosed the use of a cylindrical sound insulating member that is disposed inside the fuel passage of the fuel injector. The sound insulating member prevents the operating sound of the valve from being transmitted to the delivery pipe, thereby suppressing emission of the operating sound of the valve through the delivery pipe to the outside.
Most recently, U.S. Pat. No. 5,975,053 disclosed varying the timing, duration and amplitude of the electrical pulse to the fuel injector, in response to changes in working fluid pressure, to reduce the noise emitted.
In addition to the above-mentioned techniques used for fuel injectors, larger scale vibration reducing techniques are commonly used in various other fields, such as the aerospace and automotive body manufacturing industries. One well-known vibration damping technique is known as constrained layer damping or shear damping. Constrained layer damping is a technique wherein a damping layer of material is applied to a surface and is constrained by an outer layer having a relatively high in-plane stiffness. When the surface and the damping layer are subjected to cyclic bending due to vibration, the stiff constraining layer will constrain the damping material and force the damping material to deform in shear. The shear deformation dissipates the vibration energy and dampens the noise and vibration.
Typically, a soft aluminum tape is generously applied to the wings of aircraft or the inside of automotive body panels to dampen the vibration and noise created during travel. The tape consists of an adhesive that acts as the damping layer, and a metallic backing that acts as the constraining layer. Application of the tape to areas experiencing high vibrations will substantially attenuate the vibration and any resulting noise.
As modem vehicles continue to run more quietly, and injector noise becomes a bigger consumer issue, greater and more cost effective improvements over the prior art methods of attenuating injector noise are needed. The present invention provides an improved method for deadening the sound and vibration produced during operation of electromagnetic fuel injectors. A constrained layer damping technique is incorporated for the first time in fuel injector manufacturing to provide significant noise and vibration damping at a low cost.
To account for the materials commonly used in fuel injectors, and to keep the added costs to a minimum, the constrained layer damping technique has been slightly modified. Instead of using aluminum tape with the usual metallic constraining layer, the present invention utilizes the existing plastic overmolding of the fuel injector as the constraining layer. Therefore, only the addition of a damping layer is needed to effectively enjoy the benefits of constrained layer damping with existing fuel injectors.
The general concept remains the same, however, in that the damping layer is constrained between two relatively stiffer layers of material, namely the body portion of the injector and the plastic overmolding. As used herein and in the appended claims, the terms xe2x80x9cstiffxe2x80x9d and xe2x80x9cstifferxe2x80x9d refer to a material having a higher modulus of elasticity than the material used in the damping layer. The terms xe2x80x9cstiffxe2x80x9d and xe2x80x9cstifferxe2x80x9d are not meant to imply a specific modulus of elasticity or to otherwise limit the materials that can be used in any way.
When the relatively stiff body portion of the injector is subjected to cyclic bending due to vibration, the relatively stiff outer layer or overmolding constrains the damping material and forces the damping material to deform in shear. The shear deformation dissipates the vibration energy and dampens the noise and vibration in the injector. By adding a damping layer, preferably a viscoelastic material, between the body portion and overmolding, the benefits of the constrained layer damping technique can be realized for electromagnetic fuel injectors.
More specifically, the invention provides a fuel injector assembly including a body portion, a valve seat fixed relative to the body portion, a valve member movable relative to the valve seat, an outer layer substantially surrounding the body portion, and a damping material between the body portion and the outer layer, the damping material cooperating with the outer layer to dampen noise and vibration produced during operation of the fuel injector. Preferably, the fuel injector also includes an electrical connector mounted on the body portion, and the damping material is adjacent the electrical connector. In the preferred embodiment, the damping material is a viscoelastic material.
The invention also provides a method of using constrained layer damping to attenuate noise and vibration in a fuel injector assembly having a first stiff layer and a second stiff layer. The method includes sandwiching a damping layer between the first and second stiff layers. Preferably, the first stiff layer is metallic and the second stiff layer is a plastic that is molded over the first stiff layer and the damping layer.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.